The present invention relates to a power supply circuit for supplying a power voltage to a microcomputer, and more particularly, to a power supply circuit for a microcomputer in which a power voltage supplied from a main power source to the microcomputer is controlled.
A control apparatus using a processor such as a microcomputer is often adopted in an electric appliance such as a refrigerator, a washing machine and a video cassette recorder (VCR) in order to more accurately control various loads such as a motor. In a control apparatus for an electric appliance, a main power voltage is usually supplied by inserting a power plug into a regular power socket outlet and then various loads are turned on and operate according to key manipulation by a user.
However, a conventional control circuit having a microcomputer in an electric appliance is activated in the state where a power voltage is supplied to a microcomputer and a peripheral circuit as soon as the power plug is inserted into the regular power socket outlet. The microcomputer then awaits a user's key manipulation in such a sate. Thus, during the time when the power plug of the electric appliance is inserted into the socket outlet, the power voltage is supplied to the microcomputer and the peripheral circuit irrespective of operation of the microcomputer. This causes an unnecessary idling operation of the microcomputer. As a result, the life of the microcomputer may be shortened. Also, misoperation or failure may frequently occur when a power voltage level is suddenly changed due to some factor during the time when the microcomputer awaits a user's key operation.